Cardiac arrest refers to a state where the heart of the patient has stopped beating effectively and is no longer functioning to pump blood around the body. It is often caused by myocardial infarction. If treated promptly, cardiac arrest may sometimes reversed by cardiopulmonary resuscitation (CPR) and defibrillation. Drugs to treat cardiac arrest include epinephrine, which stimulates the heart muscle and also augments pressure in the aorta, which drives coronary perfusion. Whether epinephrine significantly improves overall survival is controversial, however, because while it may improve the chances for resuscitation, it may also cause arrhythmias and strain on the heart which increase the risk of problems in the post-resuscitation phase.
Other forms of acute cardiac insufficiency include acute heart failure and cardiogenic shock. Acute heart failure is a critical condition that is commonly seen in patients with chronic heart disease. During acute heart failure, the ability of the heart to pump blood from the lung circulation into the peripheral circulation is impaired. Cardiogenic shock is a form of shock resulting from an inadequate circulation of blood due to primary failure of the ventricles of the heart to function effectively.
Triiodothyronine, also known as T3, is a thyroid hormone. Thyroid-stimulating hormone (TSH) activates the production of thyroxine (T4) and T3. T4 is converted to T3 by deiodination. T3 affects a variety of body processes, including body temperature, growth, and heart rate. T3 has important effects on cardiac tissue. Thyroid hormones, notably T3, modulate ventricular function via genomic and non-genomic mechanisms. Cardiac stress events (cardiac arrest, myocardial infarction, etc.) are associated with steep reductions in serum T3 levels. Post resuscitation T3 level correlates highly with survival rate. T3 additionally has cardiostimulatory properties: it increases the cardiac output by increasing the heart rate and force of contraction. Overall, there is reason to believe that early bolus T3 injection could increase chances of resuscitating cardiac arrest victims, and that elevating T3 serum concentration could increase prospects of survival to hospital discharge.
T3 is not currently approved for this indication, however, and current formulations of T3 are not well suited for this purpose. Triostat® requires refrigeration, making it somewhat impractical for emergency use. Also, the concentration is low for what is needed to treat cardiac arrest. T3-albumin formulation have been described but are difficult to make, and like Triostat®, have poor stability and are poorly suited for quick administration in an emergency setting.